"Everybody with Parkinson's ultimately has a decrease in their sense of smell," Dr. Jennings said. "It's one of the very first symptoms, but not everyone who has a decrease in their sense of smell goes on to develop Parkinson's because there are many different causes for hyposmia. That's where the imaging comes in."

She presented the study at the recent International Parkinson and Movement Disorder Society (MDS) 18th International Congress of Parkinson's Disease and Movement Disorders.

PARS Study

She and her colleagues at the University of Pennsylvania in Philadelphia developed the Parkinson Associated Risk Syndrome (PARS) study to see whether they could combine olfactory testing with imaging to detect PD before clinical signs appear.

"PARS is a study utilizing a 2-tiered approach to identify hyposmic individuals with a DAT deficit and therefore at increased risk for PD," Dr. Jennings explained.

The PARS cohort includes 303 participants (203 hyposmic and 100 normosmic). The participants completed a baseline evaluation and returned for annual clinical and 123I-β-CIT/single-photon emission computed tomography at 2 and 4 years. Not all participants have completed all assessments.

At baseline, 23 (11%) of 203 hyposmic participants without PD at baseline had a severe DAT deficit (<65% of age-expected striatal binding ratio). Eight of these participants (35%) phenoconverted to PD at 2 years and 14 (61%) phenoconverted at 4 years.

An additional 14 hyposmic participants had a severe DAT deficit on imaging at year 2 or year 4, and 3 of those have phenoconverted so far, Dr. Jennings reported.

Clinical characteristics of hyposmic participants reveal that those scoring at or below the 10th percentile for age and sex on the University of Pennsylvania Smell Identification Test (UPSIT) and have a DAT deficit are more likely to phenoconvert to PD within 4 years.

Implications for Prevention Trials

"These data suggest that the PARS strategy of combining sequential assessment of olfaction and DAT imaging can enrich a population for phenoconversion within 4 years," Dr. Jennings told Medscape Medical News.

"While this strategy remains limited to research applications, it does provide a scalable mechanism to identify individuals within the general population that may be at risk for PD and would be eligible for treatment trials evaluating medications with neuro-preventative potential," she added.

"That's the critical piece. It's always been thought that we are testing these types of agents too late in the game, after there is too much pathology in the brain. So identifying people early will help to potentially make a bigger impact on this disease," Dr. Jennings said.

In a statement about these results from the Movement Disorder Society, Anthony Lang, MD, director of the Movement Disorders Clinic at Toronto Western Hospital in Canada, said, "The knowledge that comes from this study will have important implications to the recruitment of individuals for future neuroprotective trials that will hopefully have a greater chance of success than previous efforts that exclusively involved patients whose disease had already evolved to the stage of manifesting the clinical features of Parkinson's disease."